A curable adhesive and a pressure-sensitive adhesive have been increasingly widely used in various fields of building construction, manufacturing of various products, and others, along with improvement in their performance. For example, in the building construction field, a curable adhesive and a pressure-sensitive adhesive are used for adhesively attaching a building material, such as a wallpaper, a floor material, a wall material or a ceiling material, to another building material for wall, floor or the like. On the other hand, in the manufacturing field other than the building construction field and in various other fields, a curable adhesive and a pressure-sensitive adhesive are used, e.g., for: adhesively attaching a wrapping to a vehicle body; a decorative sheet to a piece of furniture; and an optical film to another optical film or a display panel.
Generally, a curable adhesive has an advantage of being capable of strong adherence, as compared to a pressure-sensitive adhesive. Typically, a curable adhesive is used in such a way that it is applied to one of a target member to be adhesively attached, such as a wallpaper, and an adherend such as a wall, and, after adhesively attaching the target material and the adherend together, left to wait for curing thereof. Due to the necessity of waiting for curing, a curable adhesive obviously has poor work efficiency. Moreover, a curable adhesive has a disadvantage that, after being cured once, it becomes significantly difficult to adjust an attachment position.
On the other hand, a pressure-sensitive adhesive is incapable of strong adherence as well as a curable adhesive. However, a pressure-sensitive adhesive has an advantage of allowing peel-off even after performing attachment once, and of being easy to correct the attachment position.
As used therein, the term “curable adhesive” primarily means a type of adhesive in which, before use, it is in a liquid phase, whereas, after being attached, it will be transformed into a solid phase. The term “pressure-sensitive adhesive” primarily means a type of adhesive having properties of both liquid and solid phases.
In recent years, a curable adhesive or pressure-sensitive adhesive sheet formed by preliminarily applying such a curable adhesive or pressure-sensitive adhesive to a sheet has also been widely prevalent. The following Patent Document 1 discloses one example of the adhesive sheet to be adhesively fixed through pressure. This adhesive sheet is configured to bring in both of the advantage of a curable adhesive, i.e., position adjustability, and the advantage of a pressure-sensitive adhesive, i.e., adhesiveness. In the Patent Document 1, a plurality of protrusion elements each made of a low-adhesive substance or a non-adhesive substance are formed on at least one surface of a pressure-sensitive adhesive layer comprised in an adhesive sheet. Thus, during attachment, the protrusions make it possible to easily perform fine position adjustment of the adhesive sheet by a function of the low-adhesive or non-adhesive substance. On the other hand, during adhesive fixing, the low-adhesive or non-adhesive substance is displaced inside the pressure-sensitive adhesive layer by a press-contact force, to thereby enable adhesive strength of the pressure-sensitive adhesive layer to be produced. In the Patent Document 1, in order to obtain this function, it is recommended to use, as a material for the protrusion elements, gauze, non-woven fabric, woven fabric, metal mesh, shaped net or the like.
The following Patent Document 2 discloses another example of the adhesive sheet to be adhesively fixed through pressure. In the Patent Document 2, a dispersion layer in which non-adhesive solid particles each having an average particle size of 10 to 40 μm are uniformly dispersed is provided on one surface of an adhesive layer, wherein approximately one half of the solid particles protrude from the one surface of the adhesive layer by a height of about ¼ of the average particle size, thereby forming a plurality of protrusions. In the Patent Document 2, it is recommended to use, as the non-adhesive solid particles: inorganic solid particles of calcium carbonate, barium carbonate, calcium sulfate, aluminum sulfate, molybdenum disulfide, titanium oxide, alumina, silica, magnesium oxide, calcium oxide, calcium hydroxide, ferrous oxide, ferric oxide, glass beads, or the like; organic solid particles of cured rubber, ebonite, lignin/phenolic resin, polystyrene, vinyl chloride resin, (meth)acrylic resin, polypropylene resin, polyethylene resin, melamine resin, urea resin, or the like; organic balloons such as urea resin balloons, melamine resin balloons, phenolic resin balloons, polyvinylidene chloride balloons, or epoxy resin balloons; inorganic balloons such as glass balloons, Silas Balloons, carbon balloons, alumina balloons, or silica sand balloons; or the like.